JPH0924523A - Mold for molding plastic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a plastic lens to be formed by reducing the error range of the surface curve of the lens, to shorten the manufacturing time and to further decrease the manufacturing cost of molding by employing a resin mold as at least one of molds instead of inorganic glass molds. SOLUTION: A gasket 11 is formed of a material such as rubber, elastomer or relatively soft thermoplastic resin, and normally of two molds 13A, 13B in combination with the gasket 11. Liquid-like curable compound raw material such as monomer is poured between the two molds 13A and 13B, and so sealed as not to be leaked. When sealing, the molds 13A, 13B are clamped from both sides by a spring-like mold clamper 15. Thereafter, the assembled gasket holding mold filled with the plastic raw material is introduced into a heating furnace as it is, and the material is cured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pair of a first mold and a second mold used for casting and molding a plastic lens.
The present invention relates to a molding die (polymerization molding die) including a mold, and more particularly to a lens molding die suitable for molding a plastic lens having at least one aspherical surface.

The fields of application of plastic lenses are:
There are spectacle lenses, camera lenses, camera viewfinders, shooting lenses, projection television lenses, lenticular lenses, sunlight concentrating lenses, Fresnel lenses, and the like.

Here, the aspherical surface means not only a curved surface defined by the following expression in a narrow sense, but also a curved surface in a progressive-focus lens and a bifocal lens.

Z = X ² / {(R + (R ² − (k + 1) X ² ) ^1/2 } + A ₁ X + A ₂ X ² + ... + A _n X ⁿ where R: radius of curvature, k: aspherical coefficient , A _n : Aspherical coefficient X: Distance from the starting point

[0005]

2. Description of the Related Art In recent years, in spectacle lenses, camera lenses, and lenses for optical use, inorganic glass lenses are being replaced with plastic lenses.

Some plastic lenses are excellent in transparency and have a high refractive index, have low dispersibility and low birefringence, are lightweight and have high impact strength and stability, and are excellent in workability and absorb water. This is because it is excellent in low colorability, easy coloring and easy dyeing.

Particularly in the field of plastic lenses, there is an increasing demand for asphericalized lenses, which are difficult to mass-produce with glass lenses.

That is, a flat / spherical lens can be manufactured at a low cost even by polishing a glass material, but an aspherical lens is expensive for a glass material due to variations in accuracy and complicated production process during mass production. This is because by using a plastic lens, it can be manufactured at low cost from an aspherical glass type, an aspherical ceramic type, an aspherical metal type or the like.

The method of manufacturing the above plastic lens includes
There are injection molding methods and cutting and polishing methods using plastic blocks, but the casting polymerization method does not have the risk of molding plastic lenses with orientation and birefringence as in injection molding, and it is a cutting and grinding method. Compared with the above, it is becoming mainstream because it has the advantage that the mass production effect is significantly large.

The cast polymerization method is a method of filling and curing a plastic raw material containing a liquid thermosetting / photocurable compound as a raw material of a plastic lens between two molds, that is, between the first and second molds. It is a method of performing molding.

Since the distance between the two molds is completely arbitrary, the following (i) is set in advance to the required distance.
A method of holding a single mold with a gasket (hereinafter abbreviated as "gasket holding method"), and a method of wrapping and holding an adhesive tape around (ii) below (hereinafter abbreviated as "tape winding method") There is).

The opposing surfaces of the two molds have a curve necessary for the lens, and this curve is formed in consideration of the shrinkage rate at the time of curing and curing the plastic lens.

[0013] In order to eliminate distortion of the plastic lens after releasing from the mold and to uniformly polymerize the plastic lens, it often takes at least several hours, usually about one day or more for curing. At that time, depending on the plastic raw material, the temperature may be gradually raised to a maximum temperature of 80 to 130 ° C. After the curing is completed, the gasket is removed, and the assembled molds are physically removed by heat shock or a wedge-shaped tool, and the plastic lens is released (taken out).

(I) Gasket holding method (see FIG. 1): The gasket 11 is made of a material such as rubber, elastomer, and relatively soft thermoplastic resin.
A and 13B are combined with this gasket 11. A liquid curable compound raw material such as a monomer is injected between the two molds 13A and 13B and sealed so as not to leak. When this is sealed, the two molds 13
Both sides of A and 13B are fixed by spring-shaped mold fixtures 15. After that, the assembled gasket holding mold filled with the plastic raw material is put into a heating furnace or the like as it is to cure the plastic raw material.

At the time of mold release, the gasket removed is
Since it has been cut or dirty, it is rarely reused, but the mold should be thoroughly washed after removal.
Make sure that there are no scratches on the surface and reuse.

There are many shapes, outer diameters, and curves of plastic lenses, and the shapes of the gaskets are different accordingly, and there is the problem that many kinds of gaskets must be prepared.

Further, the gasket material needs a certain degree of flexibility, but if the flexibility is not sufficient, the volume of the mold interval cannot keep up with the shrinkage of the plastic raw material, and peeling occurs between the mold and the plastic raw material. Occurs,
There is a problem that the trace of peeling is transferred to the plastic lens after release.

(Ii) Tape winding method (see FIG. 2): Gasket holding method and two molds 13A, 13B
The method of removing the two molds is the same, except that the method of assembling is different.

In this tape winding method, one type of adhesive tape may be used to arbitrarily determine the distance between the two molds 13A and 13B, and the tape 17 may be wound so as to be held at that distance. It can be used for various types of plastic lenses, and it does not require the labor and cost of molding and managing many types of gaskets like the gasket holding method.

The relatively thin adhesive tape is flexible regardless of its material and can follow the shrinkage of the plastic lens material, so that adhesive tapes of various materials having heat resistance can be used.

The type of the adhesive tape is not particularly limited, but the film material for the adhesive tape includes a plastic film such as polypropylene or polyester, or a metal foil such as aluminum. , Acrylic, silicone, etc. are generally commercially available. Particularly, for a lens material having a high curing temperature of a plastic raw material, a heat-resistant film such as polyester and a silicone-based pressure-sensitive adhesive having high chemical resistance are preferable as the pressure-sensitive adhesive.

In the above, the two molds used in the casting polymerization, that is, the first and second molds, are generally inorganic glass molds at present.

This glass mold manufacturing method is usually as follows.
There were (i) grinding method and (ii) transfer method.

(I) Grinding method: A glass material is melted and put into various press dies to form a pressed product as a block before polishing and cutting. Then, this pressed product is subjected to abrasive cutting in order to create the necessary flat, spherical, and aspherical curves for the lens.

(Ii) Transfer method: High-precision parallel planes are preliminarily polished and cut from a pressed product, and then the required planes, spherical surfaces,
Use a transfer mold made of metal, ceramic, etc. that has been processed into an aspherical curve, place this parallel-plane polished product on it, heat it to a temperature close to the softening temperature of glass, and transfer the flat, spherical, aspherical curve To do.

[0026]

However, the molding of the glass mold has the following problems. In particular, these problems have become remarkable because it is difficult to polish when forming an aspherical surface.

(I) In the above grinding method, each glass material press-processed product requires a considerable amount of time in the process in order to grind it after first cutting it into the required curve and then producing it. I can't expect much increase in quantity. further,
Since the abrasive cutting is performed from the individual pressed products, the curve created by each is different and unstable.

(Ii) In the above-mentioned transfer method, a parallel flat surface-polished product is placed on a transfer mold made of metal, ceramic, or the like, which has been previously processed into a required curve, and transferred by heating to a temperature close to the glass softening temperature. Therefore, mass production is possible.

However, due to the temperature distribution and the difficulty of processing the high-precision parallel flat surface-polished products, the transfer cannot be performed with the same accuracy and is unstable, and the yield rate in the manufacturing process is not so good. Absent.

[0030]

The plastic lens molding die of the present invention solves the above problems by the following constitution.

In a molding die comprising a pair of a first die and a second die used for casting and molding a plastic lens, at least one of the first die and the second die is
It is characterized in that it is formed of a resin mold having moldability and releasability with respect to the plastic lens material and has a substantially uniform thickness.

[0032]

EFFECT OF THE INVENTION The plastic lens molding die of the present invention has an aspherical curve by using at least one of the molds (if an aspherical surface is added, the resin mold) instead of the inorganic glass mold. By using one of the molds on the holding side as a plastic material that is formed with high optical accuracy, the error range of the surface curve of the plastic lens to be created is reduced to improve quality, shorten manufacturing time, and reduce the mold manufacturing unit price. Great effect can be obtained.

Although a resin mold has been used for contact lenses in the past (see Japanese Patent Laid-Open No. 6-342135), this does not suggest the resin mold of the present invention.

General plastic lens (usually, diameter:
Unlike 60 mm or more, minimum thickness: 1 mm or more, contact lenses are micro products (usually diameter: around 10 mm, thickness 0.2)
.About.0.3 mm), and its molding behavior is heterogeneous. That is, the contact lens has a lower temperature and shorter time than the plastic lens at the curing heating temperature and time, and
Unlike plastic lenses, contact lenses do not need to consider post-shrinkage of molded products.

Therefore, in the past, molding of a plastic lens by a resin mold was regarded as impossible by those skilled in the art.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) The resin mold forming at least one of the molding dies of the present invention is molded by injection molding or compression molding. In particular, if one side is a glass type and one side of the plastic lens is aspherical and the other side is spherical, the type with the aspherical surface is the resin type and the type with the spherical surface is the glass type. Is desirable. This is because it is more difficult to form an aspherical surface in the glass mold than in the plastic mold. Further, by using one of them as a glass mold, it is desirable that the shape of the entire mold can be easily maintained at the time of molding a lens described later.

The resin type material may be a colored one as long as it has good formability / releasing property to the plastic lens described later, that is, basic surface accuracy and glossiness. There is no. Preferably, a transparent material is preferable so that the liquid level can be confirmed when the polymerizable compound liquid is injected into a place where two molds are assembled.

Although not particularly limited, examples of the resin type thermoplastic resin vary depending on the lens material and include polyvinyl chloride, polystyrene, ABS resin, AS resin, methacryl resin, polyethylene terephthalate, polyamide, polyacetal, polycarbonate, poly Examples thereof include butylene terephthalate, polysulfone, polyether sulfone, polyphenylene sulfide, polyarylate, polyamide imide, polyether imide, polyether ether ketone, polyimide, and various crystalline / amorphous polyolefins.

Particularly preferred are polyethylene, polypropylene, polymethylpentene, and amorphous modified polyolefin having an alicyclic ring in the main chain, which are excellent in heat resistance and chemical resistance.

The liquid polymerizable compound used as the plastic lens raw material filled in the two assembled molds includes a compound having a low curing temperature and a compound having a high curing temperature. Compounds with low curing temperature can be used in general general-purpose resin molds, but compounds with high curing temperature are crystalline or amorphous polyolefin resins with excellent heat resistance (especially containing an alicyclic ring in the main chain). Amorphous modified polyolefin) is preferred. In addition, this liquid polymerizable compound also includes a compound having a strong solvent property and a small molecular weight that easily dissolves plastics, and an oligomer type compound having a weak solvent property and a large molecular weight. Although it can be used in a mold, a crystalline or amorphous polyolefin resin having excellent chemical resistance (particularly a modified polyolefin having an alicyclic ring in its main chain) is preferable as the compound having a small molecular weight.

Further, when the above-mentioned gasket holding method is used in molding a lens, in order to prevent liquid leakage and to fix the lens mold shape, the two molds are fixed more firmly by spring-like ones from the outside. However, when a resin having a low deformation temperature or a resin mold having a thin shape is used, a problem that a necessary curve cannot be obtained easily occurs. For this reason, the method of forming by the tape winding method is preferable because it does not require the use of a strong spring-like fixture.

The resin mold is manufactured by injection molding or compression molding which is a general molding method. Usually, the glass mold is used with a thickness of about 1.5 to 3.0 mm. However, since the plastic mold generally has a drawback that the plastic material has a weak deformation strength, it is preferable that the thickness is large. Normally, a thickness of 4 mm or more is required and the upper limit is 10 mm.
The following is assumed. If it is too thick, shrinkage is likely to occur in the center of the molding die, making it difficult to form a highly accurate die. For the same reason, the resin mold is formed to have a substantially uniform thickness.

The shape of the mold used for molding this resin mold is thick, but since it is for molding thick-walled articles, a gate opening larger than the gate opening used for molding general thin-walled articles is used. The surface polishing accuracy on the side that becomes the profile is
It is necessary to polish until it reaches an optical mirror surface accuracy. When a plastic lens, which is a transparent article, is formed, it causes a decrease in surface gloss and transparency.

(1) By using a resin having a cross-linking structure as a liquid polymerizable compound which is a raw material for a plastic lens to be filled in the two molds assembled in the present invention, a plastic lens having excellent processing characteristics and other properties can be obtained. Can be molded.

When introducing a crosslinked structure into the resin, a resin having a crosslinked structure having excellent heat resistance can be obtained by copolymerizing a compound having two or more radically polymerizable functional groups in the molecule. .

The compound having two or more radical-polymerizable functional groups in the molecule is not particularly limited, but examples thereof include divinylbenzene, diallyl phthalate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth) acrylate. Ethylene glycol di (meth) acrylate, bisphenol A-di (meth) acrylate, bisphenol A-di (hydroxyethyl (meth) acrylate), tetrabromo-bisphenol A-di (meth) acrylate, tetrabromo-
Bisphenol A-di (hydroxyethyl (meth) acrylate), triallyl isocyanurate, pentaerythritol tetrakis (meth) acrylate, pentaerythritol tris (meth) acrylate, diethylene glycol bisallyl carbonate and the like can be used.

A resin having a crosslinked structure can also be obtained by reacting a compound having two or more isocyanate groups in the molecule with a compound having two or more hydroxyl groups or thiol groups in the molecule.

The compound having two or more isocyanate groups in the molecule is not particularly limited, but for example, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, polymeric 4,4'-diphenylmethane diisocyanate, chimylene diisocyanate, Naphthylene diisocyanate, paraphenylene diisocyanate, tetramethyl xylylene diisocyanate, hexamethylene diisocyanate, dicyclohexyl methane diisocyanate, isophorone diisocyanate, lysine diisocyanate, isopropylidene bis (4-cyclohexyl isocyanate), m-xylylene diisocyanate, p-xylylene diisocyanate, It is possible to use cyclohexyl diisocyanate, tolidine diisocyanate, etc.

The compound having two or more hydroxyl groups in the molecule is not particularly limited. For example, ethylene glycol, diethylene glycol, propylene glycol, glycerobutanediol, glycerol, pentanediol, pentanetriol, hexanediol, hexanetriol, Cyclohexanediol, cyclohexanetriol, etc. can be used.

The compound having two or more thiol groups in the molecule is not particularly limited. For example, trimethylolpropane tristhiol glycolate, pentaerythritol tetrakisthioglycolate, trimethylolpropane tristhiopropionate, penta Erythritol tetrakisthiopropionate, m-xylene dithiol, p-xylene dithiol, dimercaptotriethylene disulfide, 1,10-decanedithiol,
It is possible to use 1,14-tetradecanedithiol, 1,5,10-decanetrithiol, dimercaptodiethylene sulfide, 4-mercaptomethyl-3,6-dithia-1,8octanedithiol and the like.

[0051]

EXAMPLES Hereinafter, examples conducted together with comparative examples in order to confirm the effects of the present invention will be described.

The term "part by weight" as a blending unit means "part" unless otherwise specified.

<Examples 1 to 5 and Comparative Examples 1 and 2> [First step] To 100 parts of diethylene glycol bisallyl carbonate, 3.5 parts of a polymerization initiator isopropyl peroxydicarbonate was added and sufficiently stirred, and then a 1 μm filter was used. And filtered to prepare a plastic lens raw material solution.

[Second Step] Next, using an injection molding machine "Sumitomo Nestal M III Cycap 165-75" (manufactured by Sumitomo Heavy Industries, Ltd.), various thermoplastic resins shown in Table 1 were used under various conditions. Injection molding was performed to prepare various resin molds having a thickness of 5 mm.
The mold used at that time has an optical mirror surface precision, and as an eyeglass lens, the outer diameter is 75 mm and the center thickness is 1.6 mm.
(-) It is for making a 2.50 diopter spherical lens. The screw diameter of the injection molding machine is
It is 28 mm.

[Third Process] The lens raw material solution prepared in the first process is poured into the two resin molds molded in the second process assembled by polypropylene 50 μm film acrylic adhesive tape. The resin was heat-cured under the curing condition of raising the maximum temperature to 80 ° C in about 20 hours.

From Table 1 showing this result, it is understood that the combination of the resin type material and the lens material is limited to some extent.

[0057]

[Table 1]

<Examples 6 to 9 and Comparative Examples 3 to 5> [First Step] 0.25 parts of dibutyltin dichloride was added to 100 parts of dicyclohexylmethane diisocyanate and sufficiently stirred, and then 4-mercaptomethyl-3,6. −
66 parts of dithia-1,8-octanedithiol was added, stirred and filtered with a 1 μm filter to prepare a plastic lens raw material solution.

[Second Step] Next, various thermoplastic resins shown in Table 2 were molded under various conditions with an injection molding machine "Sumitomo Nestal M III Cycap 165-75" to form various resin molds having a thickness of 5 mm. Obtained. The mold used at that time has an optical mirror surface precision with an aspherical curve, and the outer diameter is 75 m.
m, center thickness 1.2 mm (-) 3.25 diopter for forming an aspherical spectacle lens. The screw diameter of the injection molding machine is 28 mm.

[Third step] One resin mold having an aspherical curve and one inorganic glass mold having another spherical curve formed in the second step were coated with a silicone adhesive on a 38 μm thick polyethylene terephthalate film. The lens raw material solution prepared in the first step is poured into the one assembled by the adhered adhesive tape, and the maximum temperature 1 is reached in about 22 hours.
After heat-curing under a curing condition of raising the temperature to 30 ° C., it was physically released with a wedge-shaped tool to obtain an aspherical eyeglass plastic lens.

From Table 2 showing the results, it can be seen that the combination of the resin type material and the lens material is limited to some extent, and in the case of containing the filler, there is a problem in formability.

[0062]

[Table 2]

<Examples 10 to 15> [First step] m-xylylene diisocyanate 100
0.018 parts of dibutyltin dichloride was added to
After sufficiently stirring, 130 parts of pentaerythritol tetrakisthiopropionate was added and stirred, and then filtered with a 1 μm filter to prepare a plastic lens raw material solution.

[Second Step] Next, the injection molding machine "Toshiba I"
"S-50-EP" (manufactured by Toshiba Machine Co., Ltd.), various thermoplastic resins shown in Table 3 were molded under various conditions to obtain various resin molds having a thickness of 5 mm. The mold used at that time was the one used in Examples 6 to 9.
-It is the same as that used in Comparative Examples 3 to 5, and the screw diameter of this injection molding machine is also 28 mm.

[Third Step] One resin mold having an aspherical surface curve and another inorganic glass mold having another spherical surface curve molded in the second step were coated with an acrylic adhesive on a 38 μm thick polyethylene terephthalate film. The lens raw material solution prepared in the first step is poured into the assembled one by the adhesive tape prepared above, and the maximum temperature of 120 is reached in about 24 hours.
After heat curing under the curing condition of raising the temperature to ℃, it was physically released with a wedge-shaped tool to obtain an aspherical eyeglass plastic lens.

The results are shown in Table 3, and it is understood that the resin mold appearance after lens release, the lens appearance and the curve accuracy are good.

[0067]

[Table 3]

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of molding a plastic lens by a gasket holding method.

FIG. 2 is a sectional view showing a plastic lens molding method by a tape winding method.

[Explanation of symbols]

 11 ... Gasket 13A ... Mold (1st type) 13B ... Mold (2nd type) 15 ... Mold fixing tool 17 ... Adhesive tape

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Claims (4)

[Claims] 1. A molding die comprising a pair of a first die and a second die used when casting and molding a plastic lens, wherein at least one of the first die and the second die is the plastic lens. A plastic lens molding die, which is a resin die having moldability and releasability with respect to a material, and is formed with a substantially uniform thickness. 2. The plastic lens according to claim 1, wherein at least one surface of the plastic lens is an aspherical surface, and the first mold or the second mold for shaping the aspherical surface is at least a resin mold. Mold for plastic lens molding. 3. The plastic lens molding die according to claim 1 or 2, wherein one of the first die and the second die is an inorganic glass die. 4. The plastic lens molding die according to claim 1, wherein the resin mold material is a modified polyolefin containing an alicyclic ring in its main chain.